1. Field of the Invention
The present invention relates generally to an apparatus for properly adjusting the optical axes of head lamps on a vehicle. More particularly, the present invention relates to an improvement of the apparatus of the foregoing type for correctly adjusting the direction of light beams irradiated from the head lamps in response to variation of an attitude of the vehicle due to variation of a load caused when a driver rides on the vehicle or a cargo is placed on the vehicle.
2. Description of the Prior Art
FIG. 8 is a block diagram which schematically illustrates by way of example a conventional apparatus for properly adjusting the optical axes of head lamps on a vehicle. Referring to FIG. 8, the apparatus is generally represented by reference numeral 31. The apparatus 31 includes a controlling section 32 on the driver's seat side and a motor driven actuator 35 on the head lamp side. Specifically, the controlling section 32 comprises a plurality of resistors 33 and a switch 34 so as to enable one of a plurality of position voltages to be selectively set by the switch 34. On the other hand, the motor driven actuator 35 comprises a voltage comparing circuit 36 into which the position voltage which has been set by the controlling section is inputted, a motor circuit to be described later and a potentiometer 39 for detecting an angle of elevation assumed by head lamps (not shown) in the form of an elevation angle voltage. The motor circuit comprises a driving circuit 37 and a motor 38. In response to an output from the voltage comparing circuit 36, the motor 38 is driven by the driving circuit 37 to correctly adjust the angle of elevation which has been assumed by the head lamps. To this end, the direction of rotation of the motor 38 and a quantity of rotation of the motor 38 are controlled by comparing the position voltage derived from the voltage comparing circuit 36 with the detected elevation angle voltage so that an angle of elevation to be assumed by the head lamps coincides with the angle of elevation which has been set by the controlling section 32.
In addition, FIG. 9 is a block diagram which schematically illustrates by way of example a conventional motor circuit which is an essential component for the apparatus shown in FIG. 8. The conventional motor circuit is generally represented by reference numeral 31. As is apparent from the drawing, the motor circuit 31 comprises a driving circuit 37 and a motor 38. A controlling circuit 20 is arranged upstream of the driving circuit 37. In response to a command signal from the controlling circuit 20 indicative of normal rotation, reverse rotation, high speed rotation or low speed rotation, the driving circuit 37 converts the received command signal into an electric signal for driving the motor 38 in conformity with the given command.
Additionally, to prevent the motor 38 from being excessively heated due to failure of its rotation when the motor 38 is brought in a blocked state for some reason, a protective element 34 for preventing an excessive intensity of electric current from being fed to the motor 38 is arranged between the driving circuit 37 and the motor 38 in a serial relationship relative to a connection line 33a extending therebetween. It is preferable that the element 34 has positive temperature characteristics.
With respect to the conventional apparatus 31 as described above with reference to FIG. 8, optimum electrical characteristics of the voltage comparing circuit 36 are primarily taken into account but no particular consideration is taken to make the apparatus 31 itself optimum. Thus, if a connection line extending between the controlling section 32 and the motor driven actuator 35 is inadvertently earthed (i.e. grounded) due to undesirable contact with a vehicle body, it becomes impossible that an angle of elevation to be correctly assumed by the head lamps matches with the angle of elevation derived from the voltage comparing circuit 36. This leads to malfunctions such that the motor 38 is excessively heated to failure of its rotation and optical axes of the head lamps are oriented in an excessively upward tilted state, resulting in normal traffic being obstructed by dazzling light irradiated from the head lamps.
Further, with respect to the conventional motor circuit included in the conventional apparatus, since the driving circuit 37 is connected directly to a power supply source, an excessive intensity of electric current may be fed to the motor 38 when rotation of the motor 38 is blocked, causing the motor 38 to be often damaged. At this time, the motor circuit 31 needs to be repaired.